This invention relates to a process for rendering a polymer article antimicrobial, comprising contacting a chitosan solution with the surface of a polymer that contains amino-reactive functional groups as polymerized.
As evidenced by the presence in the market of numerous materials for eliminating or minimizing human contact with bacteria, there is clearly a demand for materials and/or processes that either minimize or kill bacteria encountered in the environment. Such materials are useful in areas of food preparation or handling and in areas of personal hygiene, such as bathrooms. Similarly, there is a use for such antibacterial materials in hospitals and nursing homes where people with lowered resistance are especially vulnerable to bacteria.
Chitosan is the commonly used name for poly-[1-4]-β-D-glucosamine. Chitosan is chemically derived from chitin, which is a poly-[1-4]-β-N-acetyl-D-glucosamine, which, in turn, is derived from the cell walls of fungi, the shells of insects and, especially, crustaceans. Thus, it is inexpensively derived from widely available materials. It is available as an article of commerce from, for example, Biopolymer Engineering, Inc. (St. Paul, Minn.); Biopolymer Technologies, Inc. (Westborough, Mass.); and CarboMer, Inc. (Westborough, Mass.).
Chitosan can be treated with metal salt solutions so that the metal ion forms a complex with the chitosan. Chitosan and chitosan-metal compounds are known to provide antimicrobial activity as bacteriocides and fungicides (see, e.g., T. L. Vigo, “Antimicrobial Polymers and Fibers: Retrospective and Prospective,” in Bioactive Fibers and Polymers, J. V. Edwards and T. L. Vigo, eds., ACS Symposium Series 792, pp. 175-200, American Chemical Society, 2001). Chitosan is also known to impart antiviral activity, though the mechanism is not yet well understood (see, e.g., Chirkov, S. N., Applied Biochemistry and Microbiology (Translation of Prikladnaya Biokhimiya i Mikrobiologiya) (2002), 38(1), 1-8). Additionally, chitosan is known to impart antiodor properties; see, for example, WO 1999061079(A1).
Japanese Kokai 05269181 discloses the preparation of antimicrobial polymers for contact lenses and containers for contact lenses. The reference discusses chitosan being reacted with the surface of an optically clear contact lens material. Exemplified are methacrylate/carbonate copolymers with hydroxyl functionality. In one example, chitosan is attached to the surface by graft polymerization in carbodiimide aqueous solution onto an acrylic acid layer that has been first grafted onto the contact lens. In another example, a solution of chitosan in N-methyl-pyrrolidone contacts the contact lens, and the chitosan is crosslinked.
U.S. Pat. No. 5,618,622 discloses a surface-modified fibrous filtration medium which includes hydrocarbon polymer fibers having cationic or anionic functional groups on the surfaces thereof, coated with a polyelectrolyte of opposite charge, such as chitosan. There is no mention of antimicrobial properties.
Japanese patent application JP01-0342435 discloses an antimicrobial coating agent that includes both chitosan and an emulsion or aqueous dispersion of a synthetic resin selected from among copolymers which include unsaturated carboxylic acids as monomer components and ionomers obtained by partially or totally neutralizing said copolymers with metal ions. The chitosan is mixed at a ratio of about 15 to 70 parts by weight with respect to 100 parts by weight of the aforementioned synthetic resin. The surface is thus a mixture of the chitosan and the synthetic polymer. The degree of deacetylation of the chitosan is 40-55%. Its solubility in water implies that its molecular weight is low, perhaps under 10,000. This reference also teaches away from coating an acidified solution of chitosan onto a film or sheet surface.
In co-pending U.S. patent application No. 2003/0091612, polyolefin articles are treated with an aqueous mixture of chromic acid and sulfuric acid, washed with deionized water, soaked in concentrated nitric acid, and again washed with deionized water before treatment with chitosan solution. While effective antimicrobial articles are made by this method, a simpler, more economical process is desirable.
It is therefore an object of this invention to provide an antimicrobial polymeric material and a process for producing same, said process comprising contacting a chitosan solution with a polymer surface that contains amino-reactive functional groups. Also provided are articles comprising such material.